1. Field of the Invention
This invention relates to a refractory composition and castable. The refractory composition comprises a refractory aggregate, an ultrafine refractory material having an average particle diameter size less than or equal to about 3 microns, a binder, and a dispersant, wherein all or a portion of the ultrafine refractory material comprises thermal black. This invention also relates to a refractory castable composition comprising the refractory composition of the instant invention and water in an amount sufficient to achieve a castable consistency for casting the refractory castable composition with the use of forms.
Further, this invention relates to an essentially non-slumping, high density, low moisture sprayable refractory castable composition which can be applied without forms, comprising a tempered, pumpable first component comprising the refractory castable composition as disclosed herein, and a second component comprising at least one flocculating agent that is added to the first component at the time of installation of the sprayable refractory castable composition in an amount to prevent slumping. A method of applying the essentially non-slumping, high density, low moisture sprayable refractory castable composition is provided.
2. Brief Description of the Background Art
A considerable amount of work has been done by those skilled in the art to improve the properties of refractory castables. For example, much work has been done to lower the water content required for casting calcium aluminate cement bonded high alumina and fireclay refractory castables. It is well known by those skilled ii the art that a reduction in the water content required for casting leads to higher density and lower porosity, ultimately resulting in refractory castables that perform better in service.
The reduction in water content required for casting refractory castables has resulted from the use of dispersants and ultrafine particles in combination with particle packing principles. The dispersants minimize formation of flocs that raise water requirements. More optimum particle packing has been achieved by using progressively finer particles to fill in the voids between the coarser aggregates. Without these ultrafine particles, the voids between the coarser aggregates would fill with water during casting, thus, increasing the amount of water needed in the refractory castable. It will be appreciated by those skilled in the art that a substantial reduction in the amount of water required for casting refractory castables was realized with the discovery that ultrafine particles (i.e. particles having a diameter of less than about three microns) could be included in the products when used with appropriate dispersants. The ultrafine particles used for this purpose have been ultrafine refractory materials, namely, oxides, such as for example, microsilica and finely ground alumina being the most common choices. European Patent EP 0742416 (hereinafter EP ""416) discloses a spray operation method for monolithic refractories wherein a fine powder of alumina or fumed silica having a particle size of at most three microns imparts good flowability to the mixed batch of monolithic refractories. U.S. Pat. No. 5,549,745 (Langenohl et al.) (hereinafter U.S. ""745) and U.S. Pat. No, 5,512,325 (Langenohl et al.) (hereinafter U.S. ""325) disclose a non-slumping, high density, low moisture, low cement sprayable refractory castable composition which can be applied without forms containing a solid flow aid that is microsilica, 1 to 3 micron alumina, or mixtures thereof
Despite their effectiveness in lowering water requirements for casting, there arc drawbacks to using microsilica and ultrafine alumina. For example, microsilica typically reduces high temperature refractoriness of refractory castables. In high alumina and fireclay castables bonded with calcium aluminate cement, for example, the microsilica combines with lime from the calcium aluminate cement when the castable is heated, forming low melting point glasses. These glasses cause major disadvantages such as for example, but not limited to, making the castable more prone to creep at high temperatures, decreasing the hot strength and increasing the susceptibility of the castable to chemical corrosion. In an attempt to deal with the problem of glass formation, refractory compositions with either no calcium aluminate cement, or reduced levels of calcium aluminate cement have been developed. The resulting lower lime contents reduce the amount of low melting glass that forms, but refractoriness is still not optimized because the microsilica in the matrix of the castable remain susceptible to chemical alteration and fluxing by constituents commonly found in the environments in which the castables were used. Ultrafine alumina, when used to reduce the water required for casting refractory castables, is a substantial commercial impediment because of its high cost. In addition, ultrafine alumina can have a detrimental effect on the rheology of refractory castables, in particular those that are bonded with calcium aluminate cement. Refractory castables containing calcium aluminate cement and ultrafine alumina can exhibit short working times and poor casting characteristics. While not fully understood, it is believed that the ultrafine alumina provides nucleation sites for precipitation of hydrate phases from solution during mixing and placement of the castables. It is known by those skilled in the art that alumina-lime hydrate phases form on the edges of ultrafine alumina particles in suspensions of ultrafine alumina and calcium aluminate cement in water. It is believed that to these hydrate phases affect the morphology of the finest constituents in the refractory castables, thereby adversely affecting rheology and casting characteristics.
Other ultrafine refractory oxides for reducing the amount of water required for casting refractory castables have similar drawbacks. For example, ultrafine chromic oxide is expensive and is undesirable from an environmental standpoint. Ultrafine titania is also expensive and is generally regarded as a flux in refractory systems. Thus, despite the ability of various ultrafine refractory oxides to reduce the water required for casting refractory castables, no ultrafine refractory material heretofore has been found that is wholly satisfactory from either a technical, environmental, or economic standpoint Further, it will be appreciated by those skilled in the art, that no ultrafine refractory material heretofore has been found that provides for reducing the amount of conventional ultrafine refractory oxides employed or for eliminating the use of conventional ultrafine refractory oxides to fill in the voids between the coarser refractory aggregates while at the same time maintaining particle packing principles for reducing the water content required for casting.
Therefore, in spite of this background material, there remains a very real and substantial need for a refractory composition, castable, and spray mix having an ultrafine refractory material that is capable of lowering the amount of water required for casting or spraying the refractory castable composition while at the same time reducing or eliminating the undesirable characteristics of the ultrafine refractory particles disclosed by the background art.
The present invention has met the above-described needs. The present invention provides a refractory composition comprising a refractory aggregate, an ultrafine refractory material having an average particle size diameter less than or equal to about 3 microns, a binder, and a dispersant and wherein all or a portion of the ultrafine refractory material comprises a thermal black such that the refractory composition comprises from about 2 to 15 weight percent thermal black. The present invention further provides a refractory castable composition comprising the refractory composition of this invention as described herein and water present in an amount sufficient to achieve a castable consistency.
Another embodiment of the present invention provides a method of using the refractory castable composition with forms or molds to produce a castable refractory product of a desired shape. This method provides for the manufacture of a castable refractory product comprising casting the refractory castable composition of the instant invention as described herein, to form a refractory shape or lining.
In another embodiment of this invention, an essentially, non-slumping, high density, low moisture sprayable refractory castable composition is provided that is applied without forms. This sprayable refractory castable composition of the present invention comprises (a) a tempered, pumpable first component comprising 100 weight percent of the refractory castable composition, as disclosed herein, and (b) a second component comprising a flocculating agent. The flocculating agent is added to the first component of the sprayable refractory castable composition for achieving installation of the sprayable refractory castable composition in an amount sufficient to prevent slumping.
Another embodiment of this invention provides a method of applying the essentially, non-slumping, high density, low-moisture sprayable refractory castable composition of the present invention, as described herein, on a surface without the use of forms, with a pump means and an associated hose means and an associated nozzle means comprising (a) preparing a tempered pumpable first component comprising (i) 100 weight percent of a refractory composition comprising a refractory aggregate, an ultrafine refractory material having an average particle diameter size less than or equal to about three microns, a binder, and a dispersant and wherein all or a portion of the ultrafine refractory material comprises a thermal black such that the refractory composition comprises from about 2 to 15 weight percent thermal black, and (ii) from about 3 to 10 weight percent water based upon 100 weight percent of the refractory composition, wherein the water is present in an amount sufficient to achieve a pumpable consistency of the first component to enable the first component to be pumped and applied through the pump means, the hose means and the nozzle means, (b) adding a second component comprising a flocculating agent to the first component to form a refractory castable composition, wherein the flocculating agent is added to the first component at or prior to the time of the application of the refractory castable composition through the nozzle means, (c) introducing air through the nozzle means just prior to the time of the application of the refractory castable composition and (d) applying the refractory castable composition to the surface without the use of forms.
The present invention provides a refractory composition comprising from about sixty (60) to ninety (90) weight percent of a refractory aggregate, from about two (2) to twenty-fifty (25) weight percent of an ultrafine refractory material having an average particle diameter size of less than or equal to about three (3) microns, from about one-half (0.5) to fifteen (15) weight percent of a binder, and from about five one-hundredth (0.05) to two (2.0) weight percent of a dispersant, wherein all or a portion of the ultrafine refractory material comprises a thermal black such that the refractory composition comprises from about two (2) to fifteen (15) weight percent thermal black.
Another embodiment of the instant invention provides a refractory castable composition comprising (a) one-hundred (100) weight percent of a refractory composition comprising from about sixty (60) to ninety (90) weight percent of a refractory aggregate, from about two (2) to twenty-five (25) weight percent of an ultrafine refractory material having an average particle diameter size less than or equal to about three (3) microns, from about one-half (0.5) to fifteen (15) weight percent of a binder, and from about five one-hundredth (0.05) to two (2.0) weight percent of a dispersant, wherein all or a portion of the ultrafine refractory material comprises a thermal black such that the refractory composition comprises from about two (2) to fifteen (15) weight percent of the thermal black, and (b) from about three (3) to ten (10) weight percent water based upon one hundred (100) weight percent of the refractory composition, wherein the water is present in an effective amount sufficient to achieve a castable consistency.
As used herein, the term xe2x80x9ceffective amountxe2x80x9d refers to that amount of a substance necessary to bring about a desired result, such as, for example, the amount of water needed to achieve a consistency suitable for installing the refractory castable composition of the present invention, such as for example, casting, pumping, spraying and combinations thereof.
The refractory aggregate used in the instant invention can be any suitable for linings for metallurgical vessels. For example, but not limited to, the refractory aggregate comprises at least one of an alumina, a tabular alumina, a fused alumina, a calcined aluminous, a sintered alumina, a bauxite, a bauxitie kaolin, a diaspore, a mullite, an aluminous shale, a chamotte, a silica rock, a pyrophyllite, a sillimanite, a crude andalusite, a calcined andalusite, a calcined fire clay, a crude kyanite, a calcined kyanite, a zirconia, a zircon, a chromic oxide, a silicon nitride, a graphite, a carbonaceous material, a vitreous silica, a fused silica, an aluminum nitride, a silicon carbide, a boron carbide, a titanium boride, a zirconium boride, a magnesium oxide, a magnesite, a deadburned magnesite, a spinel, a rare earth oxide, and combinations thereof, and other like refractory aggregates.
The ultrafine refractory material used in the instant invention can be any suitable for linings of metallurgical vessels. For example, but not limited to, the ultrafine refractory material comprises a thermal black alone or in combination with at least one of an alumina, a titania, a bauxite, a diaspore, a mullite, an aluminous shale, a chamotte, a pyrophyllite, a sillimanite, an andaulsite, a silica rock, an amorphous silica, a famed silica, a microsilica, a silica fume, a zirconia, a zircon, a chromic oxide, a silicon nitride, a graphite, a carbonaceous material, an aluminum nitride, a silicon carbide, a boron carbide, a zirconium boride, a titanium boride, a magnesium oxide, a magnesite, a deadburned magnesite, a spinet, a rare earth oxide, and combinations thereof, and other like ultrafine refractory powders. The ultrafine refractory material of this invention has an average particle diameter size of less than or equal to three (3) microns. All or a portion of the all ultrafine refractory material of the instant invention comprises a thermal black such that the refractory composition comprises from about two (2) to fifteen (15) weight percent thermal black.
The binder used in the instant invention can be any suitable for linings of metallurgical vessels. For example, but not limited to, the binder comprises at least one of a calcium aluminate cement, a phenolic resin, pitch, an alkali silicate, a phosphate-modified aluminum silicate, and combinations thereof, and other like binders. The alkali silicate is, such as, for example, sodium silicate or potassium silicate. The phosphate-modified aluminum silicate is commercially available as xe2x80x9cLITHOPIX AS 85xe2x80x9d from Zschimmer and Schwarz Gmbh. and Co., D-5420 Lahnstein, Rhein, Germany.
The calcium aluminate cement can be any hydraulic setting calcium aluminate cement, and preferably is utilized at a concentration of about 1 to 15 weight percent (wt. %). Such calcium aluminate cements contain mainly calcium aluminate phases, although in some cases alumina and/or rheological agents are added. Calcium aluminate cements are commercially available such as, for example, having about 40 to 90 weight percent (wt. %) alumina and about 10 to 35 wt. % calcia.
It is preferable in the instant invention to use high purity calcium aluminate cements such as, for example, those containing virtually only calcium aluminate phases and alumina without any rheology additives. Commercially available high purity calcium aluminate cements contain, such as, for example, about 70 weight percent alumina and about 30 weight percent calcia, such as, for example, xe2x80x9cCA-14xe2x80x9d available from ALCOA, Pittsburgh, Pa., and xe2x80x9cSECAR 71xe2x80x9d available from Lafarge Calcium Aluminates, Inc., Chesapeake, Va.
A cement-free binder may also be used as the binder in the refractory compositions and castables of the instant invention either alone, in combination with each other, or in combination with the calcium-aluminate cement as described herein. Such cement-free binders are well known by those skilled in the art and include such as, for example, but not limited to complex phosphates such as the hereinbefore mentioned phosphate-modified aluminum silicate, alkali silicates, organic resins or pitch. Preferably, the cement-free binder is a resin such as, for example, a phenolic resin, a pitch, or a combination thereof.
As stated hereinbefore, by employing an ultrafine refractory material having all or a portion thereof comprising thermal black, the instant invention overcomes the limitations and disadvantages of ultrafine particles previously used by those skilled in the art such as, for example, microsilica, ultrafine alumina (i.e. alumina having a particle diameter from about 0.5 to 3 microns), chromic oxide and titania. It is generally well known by those skilled in the art that ultrafine particles, such as microsilica, and ultrafine alumina, in combination with suitable dispersants, reduce the water requirements for casting refractory castable compositions. As stated herein, the ultrafine particles utilized by those skilled in the art prior to the instant invention, although capable or reducing the amount of water needed for casting the refractory composition, have certain disadvantages. For example, microsilica decreased the refractoriness of the composition or made it more susceptible to chemical attack. In addition, ultrafine alumina can detrimentally effect the rheology of the refractory castable composition. By employing a refractory composition comprising from about 2 to 15 weight percent thermal black having an average particle diameter size less than or equal to about 3 microns, the use of known conventional ultrafine particles can be effectively reduced or eliminated.
The thermal black of the instant invention is a specific type of carbon black made from natural gas or for example, but not limited to, the pyrolysis of bituminous coal. Preferably, the thermal black of the instant invention is an American Society for Testing and Materials (ASTM) Designation 1765-96 thermal black having an average nitrogen surface area from about 0 to 20 square meters per gram as defined by Classification Group Nos. 8 and 9 of the ASTM Designation 1765-96. Preferably, the refractory composition of the instant invention comprises about five (5) weight percent thermal black. As will be appreciated by those skilled in the art, thermal black is available from different sources and can be used in pelletized versions. Pelletized versions of thermal black are used with appropriate mixing to break down the pellets so that the desired effect can be achieved in the refractory composition. The thermal black source may be, for example, a natural gas source, such as the N-990 type (ASTM) thermal blacks commercially available from Cancarb Limited, Medicine Hat, Alberta, Canada, or Engineered Carbons, Inc., Borger, Tex. It is important for those persons skilled in the art to understand that the present inventors have unexpectantly found that thermal blacks when employed as the ultrafine refractory material in the refractory composition of the instant invention provide for the reduction in water required for casting of the refractory composition and also improve the physical properties of the resulting refractory castable product. Further the present inventors have found that other forms of carbon black in the form of ultrafine refractory material such as for example, furnace blacks do not produce the unexpected benefits provided by the thermal blacks of the instant invention.
With respect to the dispersant of the instant invention, it must be able to disperse the thermal black as well as the other constituents of the refractory castable composition when water is added to tie refractory castable composition. Combinations of dispersants are sometimes desirable depending on the specific constituents in the refractory castable composition. The dispersant(s) employed in the instant invention is a dispersant(s) known to those skilled in the art and include such as, for example, but not limited to anionic dispersing agents. Examples of anionic dispersing agents include, for example, but not limited to, polymerized alkyl naphthalene sulfonic acids and salts thereof and modified lignins such as, for example, lignosulfonates and salts thereof. The polymerized alkyl naphthalene sulfonic acid is commercially available as the sodium salt form under the trade name xe2x80x9cDAXAD 11xe2x80x9d commercially available from W. R. Grace and Co., Lexington, Mass. The modified lignins of the instant invention may be used in liquid and powder forms and may be derived from the kraft pulping process or the sulfite pulping process known by those skilled in the art. The modified lignins used in the instant invention, may be, for example, but not limited to, fractionated lignins in terms of molecular weight, purified or may be used in either the protonated or salt forms.
Preferably, the modified lignin is a purified desulphonated sodium lignosulfonate, such as, for example, that is commercially available under the trade name xe2x80x9cMARASPERSE CBA-1xe2x80x9d from LignoTech USA, Inc., Bridgewater, N.J. Other forms of the modified lignin of the instant invention include such as, for example, but not limited to calcium lignosulfonates available commercially in a liquid form and a solid form under the trade names xe2x80x9cNORLIG Hxe2x80x9d and xe2x80x9cWAFEXxe2x80x9d respectively, from LignoTech USA, Inc, Bridgewater, N.J.
The refractory composition of the instant invention has for each 100 weight percent of the castable solids of the refractory composition from about 0.05 to 2.0 weight percent dispersant, and more preferably about 0.2 weight percent dispersant.
It will be appreciated by those persons skilled in the art that other additives may be used in combination with the dispersants of the instant invention to affect the rheology of the castable. Such additives include such as, for example, but not limited to, boric acid or citric acid retarders. Such additives arc added in the amount from about 0.01 to 1.0 weight percent for each 100 weight percent of the castable solids of the refractory castable composition.
The amount of water used in the refractory castable composition of the instant invention is the effective amount needed to achieve a castable consistency of the constituent components of the base mix (i.e. refractory aggregate, ultrafine refractory material, binder, and dispersant) of the refractory castable composition such as, for example, from about 3.0 to 10.0 weight percent water for each 100 weight percent of the constituent components of the base mix of the refractory castable composition. More preferably from about 3.0 to 7.0 weight percent water for each 100 weight percent of the constituent components of the base mix of the refractory castable is employed to attain the highest possible density and strength of the resulting refractory castable while also ensuring proper flow during casting.
In another embodiment of the instant invention, at least one metal is added to the refractory compositions and castables, as described herein. The metal is, such as, for example, aluminum, silicon, and magnesium, and alloys thereof, and/or combinations thereof. The metals are used in powdered or granular form. The metals, in addition to inhibiting carbon oxidation at elevated temperatures, react with the thermal black at temperatures above about 1470xc2x0 Fahrenheit (F.) to form carbides which enhance bonding and therefore increase the strength of the refractory castable composition of the instant invention. The metal additions are employed from about one to ten weight percent (wt. %) based upon one hundred weight percent of the refractory composition.
In another embodiment of the instant invention, a refractory composition is provided, as described herein, that further comprises the addition of fibrous material compatible with refractory compositions as known by those skilled in the art, such as for facilitating the removal of moisture upon heating. The fibrous material is, for example, but not limited to vinyl acetate and vinyl chloride fibers commercially available under the trade name xe2x80x9cVinyonxe2x80x9d from Waker USA, Norwalk, Conn. The fibrous material additions are employed from about one-tenth (0.1) to one (1.0) weight percent based upon one hundred (100)) weight percent or the refractory composition.
Another embodiment of the present invention provides a method of using the refractory castable composition with forms or molds to produce a castable refractory product of a desired shape. This method provides for the manufacture of a castable refractory product comprising casting the refractory castable composition of the instant invention as described herein to form a refractory shape or lining.
In another embodiment of this invention, an essentially, non-slumping, high density, low moisture sprayable refractory castable composition is provided that is applied without forms. This sprayable refractory castable composition of the present invention comprises (a) a tempered, pumpable first component comprising (i) 100 weight percent of a refractory castable composition wherein the refractory castable composition comprising from about 60 to 90 weight percent of a refractory aggregate, from about 2 to 25 weight percent of an ultrafine refractory material having an average particle diameter size less than or equal to about 3 microns, from about 0.5 to 15 weight percent of a binder, and from about 0.05 to 2.0 weight percent of a dispersant, wherein all or a portion of the ultrafine refractory material comprises a thermal black such that the refractory composition comprises from about 2 to 15 weight percent of the thermal black, and (ii) from about 3 to 10 weight percent water based upon 100 weight percent of the refractory composition, wherein the water is present in an amount sufficient to achieve a pumpable consistency; and (b) a second component comprising a flocculating agent. The flocculating agent is added to the first component of the sprayable refractory castable composition at or prior to the installation of the sprayable refractory castable composition to a surface without the use of forms. The flocculating agent is added to the first component in an amount to prevent slumping. Preferably, the amount of flocculating agent added for each 100 weight percent of the first component castable solids is from about 0.1 to 2.5 weight percent.
The flocculating agent used in the instant invention can be any suitable for refractory use. For example, but not limited to, the flocculating agent comprises at least one of the agents selected from the group of an alkali chloride, an alkaline-earth chloride, an alkali phosphate, a calcium hydroxide, a calcium oxide, a calcium aluminate, a potassium aluminate, and an alkali silicate. Preferably, the flocculating agent is an alkaline-earth chloride, such as for example, calcium chloride, or an alkali phosphate, such as for example, dipotassium phosphate.
In another embodiment of the present invention, the sprayable refractory castable composition as disclosed herein is provided further comprising from about 1.0 to 10 weight percent of at least one metal, as disclosed herein.
In yet another embodiment of the instant invention, the sprayable refractory castable composition, as disclosed herein, further comprises at least one of a plasticizer (i.e. such as, for example, a ball clay), a retardant agent (i.e. such as, for example, citric acid or boric acid retarders), a fibrous material, and combinations thereof, as will be appreciated and in amounts known by those skilled in the art.
Another embodiment of the present invention provides a method of applying the essentially, non-slumping, high density, low-moisture sprayable refractory castable composition of the present invention, as described herein, on a surface without the use of forms, with a pump means and an associated hose means and an associated nozzle means comprising (a) preparing a tempered pumpable first component comprising (i) 100 weight percent of a refractory composition comprising a refractory aggregate, an ultrafine refractory material having an average particle diameter size less than or equal to about three microns, a binder, and a dispersant and wherein all or a portion of the ultrafine refractory material comprises a thermal black such that the refractory composition comprises from about 2 to 15 weight percent thermal black, and (ii) from about 3 to 10 weight percent water based upon 100 weight percent of the refractory composition, wherein the water is present in an amount sufficient to achieve a pumpable consistency or the first component to enable the first component to be pumped and applied through the pump means, the hose means and the nozzle means, (b) adding a second component comprising a flocculating agent to the first component to form a sprayable refractory castable composition, wherein the flocculating agent is added to the first component to form the sprayable refractory castable composition at or just prior to the time of application of the sprayable refractory castable composition, (c) introducing air through the nozzle means just prior to the time of the application of the sprayable refractory castable composition, and (d) applying the sprayable refractory castable composition to a surface without the use of forms. Preferably, the method as disclosed herein, comprises adding the flocculant agent to the first component through the nozzle means to form the sprayable refractory castable composition just prior to the time of application of the sprayable refractory castable composition through the nozzle means. It will be understood by those persons skilled in the art that in another embodiment of the present invention, a method of applying the sprayable refractory castable composition, as disclosed herein, is provided comprising adding the flocculating agent to the first component at a point upstream from the nozzle means, such as for example, through the hose means.
It will be appreciated by those skilled in the art that another embodiment of the method of applying the sprayable refractory castable composition of the present invention comprises adding at least one metal, as disclosed herein, to the sprayable refractory castable composition. Further, the method of the instant invention further comprises adding at least one of a plasticizer, a retardant agent, and a fibrous material, and combinations thereof, as disclosed herein, in amounts known by those skilled in the art, to the sprayable refractory castable composition of the present invention.